Method of removing from high-boiling tar acids, bodies which impart color to water-white hydrocarbon liquids



Patented Feb. 12, 2

UNITED PATENT BON LIQUIDS Howard 'A. Alves, Skokie, and Byron L. Mac-Kusick, Winnetka, 111., assignors to The Pure Company, Chicago, Ill, acorporation of No Drawing. Application July 17, 1048, Serial No. 495,208

8 Claims.

This invention relates to a method and reagent for removing weaklyacidic bodies from water-immiscible organic fluids and is moreparticularly concerned with a method and reagent for removing mercaptansirom petroleum oils.

In Patent No. 2,316,966 there is disclosed and claimed a method forremoving acidic bodies from water-immiscible fluids by contacting suchfluids with aqueous alkali solutions containing the reaction product ofan alkali and high-boiling tar acids. We have found that high-boilingacids may cause dificulties when used in the extraction of mercaptansfrom gasoline and other petroleum distillates. These tar acids containsubstances which impart to the gasoline or other oil which is treatedtherewith. objectionable color and cloudiness. Moreover, in certaininstances, alkali solutions containing these tar acids become veryviscous and even solidify at temperatures of 40 F. or lower, with theresult that emulsion dimculties are encountered during use of suchsolutions. Gasoline treated with alkali solutions containinghigh-boiling tar acids may acquire an unpleasant odor. A furtherdimculty which is sometimes experienced is the interference with theanalytical determination of the mercaptan sulfur content of the treatedgasoline. Difllculty is experienced in determining the end point duringthe titration of the gasoline using the silver nitrate-ammoniumthiocyanate titration method disclosed in the May 13, 1941 AnalyticalEdition of "Industrial and Engineering Chemistry, volume 13, page 298,in an article by Bell and Agruss entitled Analytical procedure formixtures of organic sulphur compounds."

We have discovered that all of the foregoing dimculties can beeliminated if aqueous alkali solutions of the high-boiling tar acids areblown with air or other free-oxygen containing gas for a suiflcientperiod of time to convert the colorimparting bodies contained therein toproducts which are readily extractable therefrom by means of low-boilinghydrocarbons and then washing the blown solution with sufficientlow-boiling hydrocarbon to remove the objectionable bodies therefrom.

An object of the invention is to provide an improved method for removingweakly acidic bodies from otherwise neutral organic water-immisciblefluids.

Another object of the invention is to provide a. method for removingfrom high-boiling tar acids, constituents which are objectionable whentar acids are used as solubility promoters in alkali mercaptane fromhydrocarbon or other substantially neutral water-immiscible fluids.

A still further object of the invention is to provide an improvedsolubility promoter for use in extracting weakly acidic bodies fromorganic water-immiscible fluids.

Other objects of the invention will appear from the followingdescription.

In the low-temperature, by-product, destructive distillation of coal,there is ordinarily contained a dark liquid called coal tar which upondistillation produces oils of diflerent boiling ranges and a residualpitch. It is common practice in the coal-tar industry to distillcoal-tar into several fractions one being light oil, boiling up to about200 0., another known as middle oil boiling from about 200 to 250 C., athird fraction known as solutions to remove weakl acidic bodies such as65 heavy oil boiling from about 250 to 300 C., and a fourth fractionknown as anthracene oil boiling from about 300 to 350 C. It is commonpractice to treat fractions with aqueous solutions to remove therefromthe acidic substances contained therein. The resulting aqueous alkalisolution is neutralized with acid to recover the acidic substancesextracted from the various oil fractions. The

acidic substances are then fractionated to obtainvarious phenols, suchas, phenol. cresols and one or more xylenols. In the fractionation, theseparation is made between those constituents boiling below and aboveapproximately 220 C. The residual liquid from the fractionation of thetar acids is the material herein referred to as "highboiling tar aci andshows the following dis tillation analysis:

Initial boiling point 5%- off 10% of? 20% off 30% oil 40% off off oiToff off off nfi 375 Dry point 400 A solution was prepared, usinghigh-boiling tar acids made in the manner just set forth and obtainedfrom the Reilly Tar 8: Chemical Corporation by mixing together 20% drysodium hydroxide, 20% high-boiling tar acids and 60% of water, byweight. The resulting solution was not entirely homogeneous, butcontained liquid or solid material which had a shiny appearance. 300 cc.of Dubos cracked gasoline from Texas crude oil wasagitated with 7% byvolume of thesolution and the resulting gasoline was coloredyellowbrown. The treating solution continued to 1 part the yellow-browncolor to successive batches of gasoline. In addition, the gasoline wascloudy. An attempt was made to determine the mercaptan sulfur content bythe silver nitrate-ammonium thiocyanate titration method, but'considerable difllculty was experienced in determining the end point ofthe titration. Moreover, emulsion difficulties were encountered when anattempt was made to counter-currently contact gasoline with the treatingsolution in a countercurrent contact tower.

A treating solution made as Just described was contacted with anotherportion of the same gasoline in a counter-current treating tower in aratio of 7.6 volumes of solution to 100 volumes of gasoline. The treatedgasoline had a yellow-brown color and a bad odor. The treating solutionwas then regenerated by first diluting with water and boiling until thesolution reached its original volume before dilution. Air was then blownthrough the solution for a period of approximately six hours while thetemperature was maintained at about 160 to 170 F. The resulting solutionwas then washed with gasoline and again used to ex tract mercaptans fromanother sample of the same gasoline, using 7.6 volumes of treatingsolution to one hundred volumes of gasoline. The gasoline beforetreatment with the treating solution contained .088% by weight ofmercaptan sulfur and .013% by weight of disulfide sulfur. Aftertreatment with the solution. the gasoline contained .005% by weight ofmercaptan sulfur and .012% by weight of disulfide sulfur. Not only wasthe solution extremely effective in removing mercaptans from thegasoline, but it did not cause oxidation of sulfur compounds todisulfide and it did not impart an objectionable odor or color to thegasoline.

In carrying out our invention, we prefer to prepare a treating solutioncontaining alkali metal hydroxide and high-boiling tar acids, heat thesolution to approximately 200250 F. and preferably to approximately theboiling point thereof and blow air or other oxygen containing gastherethrough until the color-producing bodies in the solution areconverted to a form where they are readily extractable therefrom withgasoline. When air is used, it will generally require from one to tenhours to complete the blowing. The'sufiiciency of the air-blowing can bedetermined by cooling a sample of the blown solution to atmospherictemperature and washing it thoroughly with 20 volumes of gasoline ofgood color. This washing should remove from the treatin solutionsubstantially all of the color-producing bodies if the blowing has beenadequate. The washed gasoline is decanted from the treatin solution andthe treating solution is again mixed with a similar amount of gasolineto see if the asoline goes off color. If the color of the second batchof gasoline is substantially unaffected, the blowing is sufficient. Ifthe gasoline is discolored, the blowing must be continued.

Although we prefer to carry out the blowing of the treating solution attemperaturesapproximating the boiling temperature of the solution, theblowing may be conducted at lower temperatures ranging from appromatelyc F. upward. However, at lower temperatures, the length of the blowingrequired is considerably extended.

Higher temperatures than the normal boilin temperature of the solutionmay be resorted to in the air-blowing operation if the. operation isconducted under pressure. It may be necessary to add water to thesolution from time to time during or at the end of the blowing operationto compensate for water which escapes with the air.

After it has been determined that the solution has been blownsufficiently. it is contacted with approximately 20 volumes oflow-boiling hydrocarbons such as those boiling within the gasolineboiling range or liquid propane, butane or mixtures thereof, in order toextract the objectionable color-producing bodies from the treatingsolution. The solution is then ready to be used to treatwater-immiscible liquids to remove weakly acidic bodies therefrom. Thewashing liquid can be recovered for further use by distillation and/orfiltration through fuller's earth or similar adsorptive clay to removethe color bodies therefrom.

If desired after the blowing of the solution to convert thecolor-producing bodies into readily extractable constituents, instead ofextracting these bodies from the blown solution in a separate step, thesolution may be used in a treating operation without previous washing.In such case, the first portion of gasoline or other liquid treated,will extract the objectionable color bodies from the treating solution.This first portion may be segregated and separately treated if desired.

If the objectionable color-producing bodies are not removed from thetreating solution or from the high-boiling tar acids, the treatingsolution continues to impart to the gasoline or other liquids to betreated, an objectionable color and odor for a long period of time; evenafter repeated regeneration of the treating liquid by means of steam orboiling with water.

Although for purposes of demonstrating the invention we used a solutionmade by mixing together 20% of sodium hydroxide, 20% of air blownhigh-boiling tar acids and water, the composition of the solution mayvary within wide limits. In order to obtain appreciable removal ofmercaptans from hydrocarbon oils the treating solution should contain atleast 5% by weight of free alkali metal hydroxide, i. e. alkali metalhydroxide over and above that necessary to react with other constituentsof the solution, and at least 5% by weight of high-boiling tar acids,but preferabl in excess of 10%. Either sodium or potassium hydroxide ora mixture thereof may be used as the alkali metal hydroxide. Care shouldbe exercised to keep the free alkali hydroxide concentration of thesolution belowthe point at which the solution becomes so viscous as tocause emulsion difliculties during the treating steps. Free sodiumhydroxide concentrations up to 20% by weight and free potassiumhydroxide concentrations up to 25% by weight are satisfactory. Thetreated tar acids may be added to the solution as such or in the form ofalkali metal salts. The tar acid content of the solution may extend upto the maximum amount which is compatible with the solution and willvary with the alkali concentration of the solution. Othersolubilitypromoters such as phenols, particularly cresols, low boiling fatty acidsand naphthenic acids may be used as components of the treating solution.

Treatment of gasoline and other hydrocarbc distiliates by meansof alkalisolutions containing tar acids prepared in accordance with our inventionmay take place at ordinary atmospheric temperature and preferablywithinthe range of approximately 40-100 F. The ratio of treating solution tooil undergoing treatment will depend on the nature and amount of acidicbodies contained in the oils, but in general, a. ratio of to 20% oftreating solution by volume based on the oil undergoing treatment can beused with good results. The treating solution can be regenerated byboiling or by stripping the absorbed acidic constituents therefrom bymeans of steam at temperatures of approximately 220-250 F.

It is claimed:

1. The method of preparing a treating agent for removing weakly acidicbodies from organic, water-immiscible liquids which comprises preparinga solution of high-boiling tar acids in aqueous alkali, and blowing thesolution at elevated temperature with free oxygen-containing gas untilthe color-imparting bodies contained therein can be readily extractedwith liquid-lowboiling hydrocarbons and extracting said colorimpartingbodies therefrom by means of low boiling hydrocarbon liquid.

2. The method for preparing a treating agent for removing weakly acidicbodies from organic, water-immiscible liquids which comprises preparinga solution of high-boiling tar acids in aqueous alkali and blowing thesolution with air at approximately the boiling temperature of saidsolution for a period of time ranging from 1 to hours and extracting theresulting solution with liquid low boiling hydrocarbons.

3. The method of removing from high-boiling tar acids, bodies whichimpart color to water white hydrocarbon liquids comprising blowing saidtar acids at elevated temperature, mixed tract oxidized color-impartingbodies and separating the extract from the said alkali metal hydroxidesolution.

4. Method in accordance with claim 3 in which the solution is blown withair at approximately the boiling point of the solution.

5. The method of simultaneously removing color-imparting bodies from anaqueous alkali solution containing high boiling tar acids and removingmercaptans from low boiling-hydrocarbon oils which comprises contactingsaid oil with an aqueous solution containing free alkali hydroxide andhigh-boiling tar acids in sufflcient amount to enhance the ability ofsaid solution to extract mercaptan from said oil, said solutions havingbeen air blown at temperatures or approximately the boiling point of thesolution for a suflicient period of time to oxidize the color-impartingbodies therein to substances which are readily extractable therefrom-with low-boiling liquid hydrocarbons.

6. The method of simultaneously removing color-imparting bodies from anaqueous alkali solution containing high boiling tar acids and removingmercaptans from hydrocarbons boiling within the gasoline range whichcomprises contacting said hydrocarbons with an aqueous solutioncontaining not less than 5% by weight of free alkali metal hydroxide andnot less than 10% by weight of high boiling tar acids, said solutionhaving been blown at a temperature above 150 F. under suflicientpressure to keep it in liquid phase with air until the color-producingbodies contained therein can be removed by washing with 20 times itsvolume of gasoline boiling range hydrocarbons.

7. Method in accordance with claim 6 in which the solution is blown at atemperature of approximately 220-250 F.

8. Method in accordance with claim 3 in which the solution is blown withair at a temperature above F. under suflicient pressure to keep thesolution in liquid phase.

HOWARD A. ALVES. BYRON L. MacKUSICK.

